High vacuum pump



Feb; 3, 948. A. H. ROSENTHAL 2,435,548

' HIGH VACUUM PUMP Filed Nov, 5, 1945 2 Sheets-Sheet 1 17 1g 43 4Q 36 4151 42 8 @y iaj. .53 39 74 Q 76 7 ,135 g3;

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HIGH VACUUM PUMP Filed Nov. 5, 1943 2 Sheets-Sheet 2 4D ('3' 2- r: a 1315 11 I: 113

INVENTOR 140011 15 H. POSENTHAZ ATTORNEY Patented F ch. 3, 1948 HIGHVACUUM PUMP Adolph n. Rosenthal, New rel-k, N. Y., assignor to ScophonyCorporation of America, New York, N. Y., a corporation of DelawareApplication November 5, 1943, Serial No. 509,144

14 Claims. (Cl. 230-1) This invention relates to a method and apparatusfor rarefying vapors or gases, in particular air, within confined spaceand thereby producing a vacuum of desired high degree. Si'ngleormulti-stage pumps have been suggested for this or vapor used as aworking medium which depends on the prevailing temperature. The lowpressure obtainable by this type of pump is thus limited and they areused mostly for producing vacua of moderate degree and as auxiliary orbacking pumps for other, more eflicient vacuum 'Another type of pumpused in the vacuum technique for producing moderate vacua is of thereciprocating piston type, the efliciency of which was increased byfilling its dead spaces or clearances with liquids of high boilingpoint, such as oil or mercury. Here again the vapor pressure of theseliquids limited the degree of vacuum attainable by their use; leakagelosses in the valves and through the packings of the piston rod, etc.,caused additional diificulties. The vacuum attainable by this type ofpump is considerably better than that of ejector pumps, but does notsuffice to produce high vacua as required in many branches of todaysvacuum technique and they are used, therefore, as auxiliary or backingpumps to produce a pre-vacuum for more effective pumps of other types.Rotating pumps of the vane and gear type are of similar efiect and use.

Vacuum pumps which permit the production of extremely high vacua, i. e.extreme rarefaction and consequential extremely low pressures of a gas,operate either on the principle of gas diffusion into streaming,particularly injectedv vapors of mercury or oil, or on the molecular"principle. The performance of the vapor diffusion pumps is limited bythe vapor pressure of the working medium, and their operation iscomplicated by the heating means required for vaporizin'g the workingmedium, and by cooling means. The "molecular pumps make use of the quitefundamentally changed behaviour of gas when its rarefaction is extendedso far that the mean free path of the individual gas molecules is largerthan the dimensions of the space in which the gas is confined.

At a given temperature, the pressure of a gas is proportional to thenumber of gas molecules in a unit of volume. At atmospheric andconsiderably lower pressure, the gas molecules within a unit of volumefly irregularly in every direction, collide frequently and changethereby the directions of their flight. Hence the direction of flight ofthe individual gas molecule is undefined. Even if an impact isexerted-upon it in a certain direction, its thus directed path will beterminated soon upon collision with other molecules. However, if therarefaction of the gas exceeds a certain degree (and the gas pressure isthereby reduced below a certain value), the average or mean path which amolecule follows freely without colliding with another one, is extendedso far that its hitting upon and being reflected by the wall of theconfined space is much more likely than its colliding with another gasmolecule. In such a state of rarefaction and at such a low pressure inthe gas, the individual gas molecules are therefore eminently capable ofbeing directed by a moving surface upon which they impinge. The meanfree paths of the molecules of various gases used in the vacuumtechnique at decreasing gas pressures have been calculated and verifiedby experiments, and are therefore well known. With air, a state in whichthe mean free path of its molecules exceeds usual dimensions of spacesin which the air is to be rarefied, is attained at pressures of about0.001 mm. mercury column, and such and lower air pressures are commonlytermed a true high vacuum.

The molecular pump type utilizes this behaviour of gas under lowpressure. The molecules of a pre-rarefied gas are admitted to the pumpspace and permitted to impinge upon the circumference of a rapidlyrotating drum which reflects as well as imparts to them a velocitycomponent in the direction of its rotation; the thus repeatedlyreflected molecules are transported towards and through the outlet ofthe pump space into another space. As a consequence, the number of gasmolecules in that other space is increased, resulting in increase ofpressure, while the space from which the gas molecules fiew upon thecircumference of the rotating drum is depleted of gas molecules and thepressure therein reduced, finally resulting in an extremely high vacuum.The efliciency of this type of pump and the degree of vacuum attainableare limited by the maximum circumferential speed of the rotating drum onwhich its efiect depends, by inevitable leakage in the bearings of thedrum shaft, etc.

The invention is concerned with a method of rarefying vapors and gasesand an apparatus or pump therefor which also utilizes the behaviour of asuificiently pre-rarefied gas (or vapor) just described, viz. that itsmolecules can be directed and accelerated efiectively by mechanicalaction upon them, and it is an object of the invention to improve vacuumpumps, particularly high vacuum pumps working on this "molecular"principle.

In particular, it is an object of the invention to eliminate thedisadvantages attendant upon diffusion or diffusion-ejector high vacuumpumps which use vapors of boiling liquids, and to do away with theheating and cooling means of those pumps. According to the invention, noliquids and vapors are used at all for producing the high vacuum.

It is another object of the invention to eliminate rotating orreciprocating members of a high vacuum pump, such as used heretofore inthe rotating molecular pump or with reciprocating piston pumps in whichthe clearance is reduced by means of high boiling liquids. Thereby thedifllculties attendant upon these pumps as to fast moving parts andleakages in bearings of a drum shaft or packings of a piston rod, etc.are avoided.

It is still a further object of the invention to increase the efficiencyof the mechanical action upon the gas molecules of a pre-rarefied gas,by subjecting them to an immediate directing impact by a vibratingsurface rather than reflection by a surface which rotates at high speedin one direction.

It is a further object of the invention to utilize the efiect ofsupersonic vibrations of a mechanical vibrator upon gas, for producinghigh vacua or extremely low gas pressures.

It is still another object of the invention to provide a, method ofproducing high and highest vacua and a relatively small and compactapparatus therefor, the active elements of which are entirely within thespace in which the gas undergoing rarefaction is confined, arestationary and actuated electrically, and the intensity of action ofwhich can be regulated electrically from outside the confined spacewithout resort to anymovable part passing a wall of that space.

These and other objects of the invention will be more clearly understoodwhen the specification proceeds with reference to the drawings in whichFig. 1 shows rather schematically in vertical cross-section, with partsin elevation, a singlestage high vacuum pump according to the inventionand diagrammatically an electric circuit for exciting supersonicmechanical vibrations of a vibrator used by the invention, Fig. 2 invertical cross-section and at a larger scale the arrangement of apiezo-electric vibrator in the example of Fig. 1, Fig. 3 in verticalcross-section and partly in elevation a two stage pump according to theinvention, Fig. 4 in a similar manner a multistage pump according to theinvention connected with a manifold for evacuating bulbs, and Fig. 5 invertical cross-section and Fig. 6 in a view from below, the arrangementof bailles in back of a vibrator unit as used by the invention and shownin Fig. 1.

Referring to Fig. 1, there is shown as a vessel or container to beevacuated, a bel-Jar l0, e. g. of steel or glass, placed upon a pumpplate I I, e. g. of steel, the upper surface of which is preferablyground and polished so as to provide an air-tight fit with the equallyground lower edge of belljar l0. Sealing wax or a gasket l2 may beapplied between the bell-jar and pump plate. A pipe I3 is air-tightlyfitted into a corresponding aperture of plate II and conically widenedat its lower end IS. A duct provided with a manually operated valve itpasses another aperture in plate I I and is air-tightly mounted therein;valve l4 permits the interior of jar Ill to be connected with and shutoff from the surrounding at; mosphere.

A longitudinal vessel II, c. g. of steel, open at and tapering towardsboth of its ends engages with its uppr end II the interior of conicalend l5 of pipe or duct l3. The engaging surfaces of,

the ends l5 and I8 are preferably ground into one another in order tosecure an air-tight con nection; they may be sealed additionally with asuitable sealing compound. The lower end l8 of vessel I1 is conicallyenlarged and fitted upon an equally conical end I! of an intake duct 20leading to the suction side of a pre-vacuum pump 2 I. The engagingsurfaces of the conical parts l8, I8 are preferably ground into oneanother and sealed, in order to secure their air-tight connection.Vacuum pump 2| is of any type suitable to produce a pre-vacuum, such asa vane-pump, and driven by an electromotor 22. 23 is an outlet of vacuumpump 2|.

A mechanical vibrator capable of being electrically excited tosupersonic vibrations of suitably high frequency, preferably of betweenabout 100,000 to 10,000,000 cycles per second is arranged within' vessel[1. The vibrator consists in this exemplification of the invention of apiece 24 of piezo-electric material, such as quartz, tourmaline,Rochelle salt, etc. The piece is cut from crystalline piezo-electricmaterial in well known manner, along two parallel planes which areperpendicularto a polar axis of the piezo-electric crystal; such cuts ofquartz crystals are known for instance as Curie-cut" or X-cut. Somepiezo-electric crystals, e. g. quartz crystals, exhibit more than one,e. g. three polar axes, and the distant parallel planes along which thepiece is cut from the crystal, may be perpendicular to any one of them.The direction of the mechanical resonance vibrations excited in a thuscut piece' may be parallel to the selected polar axis andthereforeperpendicular to said parallel planes. The vibrations in the directionof one of those polar axes produced by an alternating electric field inthe direction of this axis are termed longitudinal or thicknessvibrations, and their resonance frequency depends mainly on thethickness of the piece. Although other types of vibrations, such astransverse vibrations may be produced and utilized, thickness vibrationsare generally preferred. The vibrations can be excited by application ofrecurrent electric impulses or oscillatory energy, particularly of asinusoidal voltage to suitable electrodes placed upon two distantparallel planes, and the vibrations are particularly strong if thefrequency of the alternating electric voltage essentially equals themechanical resonance frequency of the piece within narrow range. Thecrystal piece may also be excited to vibrations of an odd integermultiple frequency of its fundamental resonance frequency, and such oddharmonic vibrations can be used to advantage by the invention. Theenergy of the mechanical resonance vibrations depends upon that of theapplied electric impulses; voltages from several hundred to severalthousand volts can be used.

Now referring to Figs. 1 and 2, it is assumed that crystal piece 24 iscut from a. quartz crystal in such manner that thickness vibrationsresult, and that it has the shape of a cylindrical plate the cylindricalcircumference of which is parallel and the plane front surfaces of whichare perpendicular to the selected polar axis. Front surface 25 isessentially freely exposed and contacted near its edge only by aring-shaped elecceramic material.

trode 25; the rear surface of piece 24 is covered by an electrode 21.The ring and full electrodes may be cut from metallic sheet material andpressed or cemented onto piece 24, or one or both of them may be appliedto piece 24 by vacuum evaporation or sputtering upon the respectivesurface suitable electrode material such as copper, aluminum, etc. Theelectrode on front surface 25 may also consistot a thin metallayercompletely covering that surface and produced or applied in a similarway as the rear electrode 21.

Crystal piece 24 with electrodes 25, .21 is mounted within a cylindricalrecess 28 of an electrical insulator 29, for instance of glass or Recess28 is continued by a larger recess 30 into which a metal ring 3| isfitted, e. g. screwed or cemented. Ring 3| is supported in vessel l1 bymeans oi four radial spokes 32 which in this exem'plification of theinvention are made particularly cast in one piece with the lower part ofvessel .|1.

The outer contour oi! insulator 29 may be streamlined and is continuedby the smooth outer surface of ring 3| into its opening 33 in front ofsurface 25 of vibrator 24, leaving a narrow passage 16 between theinsulator'and the wall of vessel l1. A hole or bore 34 in insulator 29is passed by a conductive bolt or rod 35 whose lower end projects intorecess 28 to form a rivet 36 which holds in place a flat spring 31. Thisspring comprises in this example four springy arms which rest uponelectrode 21 and press piece 24 against the inwardly projectingrim ofring 3|. The upper end 38 of rod 35 is screw-threaded and projectsoutside the top of insulator 29 and recess 39 in it. Two nuts 48. 4| arescrewed upon the screw-threaded end 38. Nut 48 engages recess 39 andholds rod 35 and spring 31 in place relative to insulator 29. Aconductor 42 is clamped between nuts 48 and 4| and leads to a rod 43passing an insulator 44, for instance of lass or ceramic material. Thisinsulator comprises a cylindrical portion passed through a hole 45 inthe wall of vessel l1; an insulating ring 45 is fitted upon theprojecting inner end of that cylindrical portion and held in place bynut 41 screwed upon the inner end of rod 43. The end of lead 42 isconductively connected with rod 48. Nuts 48, 49 are screwed upon theouter end 01 rod 43 and a terminal 58 is clamped between them. A vacuumsealing compound may be suitably applied in all the gaps betweeninsulating ring 45, insulator 44, wall of vessel l1, rod 43, and nuts 41and 48.

A conical hood 5| is slipped over and fastened at 53 to the top ofinsulator 29. and covers the projecting end 38 of rod 35, and the nutsthereon. Thereby the streamlined shape of the vibrator unit is completedand back-reflection of gas molecules toward jar I5 is prevented. Thehood may consist of metal or insulating material; in the former case,lead 42 is to be insulated from the hood. Hood 5| is provided with a,few small holes (not shown) through which its interior communicates withthe surrounding space. Hood 5| can be dispensed with if the end 38 andnuts 48, 4| are fitted into the streamlined contour.

A set of bailles 54 can be arranged above hood 5| as shown more indetail in Figs. 5 and 6: they also serve to prevent back reflection ofgas molecules into jar l0.

Any type of generator of recurrent electric impulses or oscillations canbe used for exciting anem a the mechanical resonance vibrations of piece24. Fig. 1 exemplifies the diagram of a Hartley circuit. It comprises inits most simple form and essentially a triode 55 with cathode 55, grid51 and plate (anode) 58. 59 is a (regulable) source of current forheating cathode 55; 58 a (regulable) source of plate current; 5| amake-andbreak switch for starting and interrupting the oscillations; 52a resistance in the heating circuit of the cathode from which, throughleak resistance 53 and adjustable tap 54, a desired bias of grid 51 canbe derived; 55 is a block condenser;

55 a self-induction coil and 51 an adjustable condenser, and togetherthey form an adjustable oscillation circuit which determines thefrequency and maintains the generation of the oscillations; 58 is an(adjustable) tap for connecting a desired point of coil 55 with thepositive terminal of source 58. One end of coil 55 and condenser 51 isconnected by conductor 59 with terminal 58, while the opposite end ofcoil 55 and condenser 51 is connected by conductor 18 with terminal 88clamped between nut 14 and flange 12. Thus the oscillating voltagegenerated is applied through conductor 59, terminal 50, rod 49, lead 42,rod 35 and spring 31 to electrode 21, and through conductor 18, terminal88. vessel l1, spokes 32, ring 3| to the other electrode 25. If anode 58is to be grounded, conductor 59 will be connected with terminal 88 andvessel l1, and conductor 10 with terminal 55. However this connectionbe, by adjusting condenser 51, the frequency enerated can be varied; byadjusting tap 54 and/or tap 58 the oscillation energy generated andthereby the mechanical vibration energy of piece 24 can be varied. Othermeans and arrangements for generating supersonic oscillations of desiredhigh frequency and energy can be used instead of the ones illustrated.

In the example shown in Figs. 1 and 2, vessel I1 is sub-divided into anupper and lower portion which are connected by means of flanges 1|, 12and bolts 13 provided with nuts 14. A vacuum sealing compound 15 may beprovided between the contacting flanges 1|, 12. This sub-divisionpermits convenient mounting of the vibrator unit and its supports withinvessel l1, and replacing or exchanging of the former for repair ordesired change e. g. of frequency and/or exposed active surface area.

In operation, after bell-jar l8 has been airtightly positioned upon pumpplate II and valve l4 closed, the backing pump 2| is started byswitching in motor 22, and gradually rarefies the gas (air) enclosed inthe first or upper confined space comprised of the interior of jar l8,pipe l3 and space 18 within vessel I1 back of insulator 29 and thevibrator unit, as Well-as in the second or lower confined space 11within vessel H in front of the freely exposed surface 25 of vibrator24; the first named confined space communicates through passage or gap15 with the second confined space and the latter through duct 23 withthe suction or intake side of pump 2 I.

After the gas has been rarefied in all the communicating confined spacesnamed almost to the limit of low pressure attainable by the backingpump, e. g. 10- to 10- millimeters mercury column, switch 5| is closedand thereby vibrator 24 and its surface 25 excited to supersonicvibrations of adjusted energy. At the low pressure produced by pump 2|,the gas (air in this example) is rarefied to an extent that the averagepath of free flight of its molecules, i. e. until they collide withoneanother, or their "mean free path is in the order of or exceeds thedimensions oipassage 16.

It will be seen from Figs. 1 and 2 that vibrator 24 is completelyscreened or covered against the first confined space as defined above,particularly space 18, and also against passage 16 by insulator 29 andring 3i. Its surface 25 is solely exposed toward the second confinedspace 11. The direction of the supersonic vibrations of surface 25 isessentially perpendicular to it, and their effective outward stroke isdirected toward space 11 and away from passage 16.

If gas molecules impinge upon the vehemently vibrating surfaces 25, theimpact of the latter imparts to them a velocity component in thedirection of those vibrations, viz. toward space 11 and away frompassage 16. These gas molecules are thereby projected into space 11 inthe direction of arrows 15 and, since surface 25 vibrates with highvelocity and acceleration at supersonic high frequency and it impactsupon impinging gas molecules recur extremely fast, the number ofprojected gas molecules will be considerable and result ininstantaneous, at least local reduction of gas pressure in front ofsurface 25 and sufliciently close to the discharge end of passage 16into space 11, to cause diffusion of gas molecules from the firstconfined space, including space 18, through passage 16 in the directionof arrows 19 toward the front of vibrator 24. Many of the thus diffusedgas molecules impinge upon surface 25 and are projected into the secondconfined space 11 wherefrom they are removed by backing pump 2I. Somediffused gas molecules will hit the wall of vessel I1 and be reflectedtoward surface 25 which throws them into space 11 wherefrom they areremoved by pump 2I. Only a few diffused gas molecules will returnthrough passage 16 into space 18. Thus the ratio of returning orre-diifusing gas molecules to those effectively removed from space 11will be very small, particularly if the passage space or area 16 issufliciently small compared with the effective area of surface 25.

The concurrent phenomena of gas removal just described recur in thefrequency of the vibrating surface 25. By proper choice and adjustmentof that supersonic frequency and its amplitude, depending inter alia onthe kind of gas or vapor undergoing rarefaction, the dimensions of thespaces and the degree of high vacuum to be produced, optimum effects canbe attained and the speed of evacuation controlled. The frequency can bevaried stepwise by changing the frequency of the oscillation generatorfrom a value corresponding to the fundamental mechanical resonancefrequency of the vibrator 24 to any odd (higher). harmonic thereof, e.g. by adjusting condenser 61. The desired amplitude of the mechanicalvibrations can be obtained by adjusting positions of tap 64 on resistor62.

If it were possible to direct and project all the molecules impingingupon surface 25 into the backing pump, no back-diffusion could occurthrough passage 16, and an almost complete vacuum could be attained. Inpractice, the backdiffusion and the low pressure limit of the backingpump also limit the degree of highest vacuum attainable in the firstconfined space includin bell-jar I by means of a single vibrator pumpstage. If higher or highest vacua and/or pumping Speeds are desired, twoor more vibrator units can be arranged in series. Fig. 3 exemplifies thearrangement in series of two such vibrator units.

Insulator 90 is cone-shaped with its point within space 18 of vessel 82,and is provided with a, lateral bore 9| through which a lead 02 ispassed the end of which contacts spring 01 and is riveted with it tobolt 93 positioned within an axial bore 94 of insulator 90. Lead 92projects air-tightly through an insulator 94 which is airtightly sealedby means of a vacuum sealing compound 95 into an opening 96 of vessel82. The outer end of lead 82 is screw-threaded and two nuts 91 and 98screwed upon it between which terminal 50 is clamped.

Piezo-electric vibrator 24 is cut and shaped in the same manner asdescribed with reference to Figs. 1, 2 and provided with electrodes 21.20

and supported by the projecting rim of ring 8|.

The tapered upper end 8I of vessel 82 fits into the lower end I5 of pipeI3 connected e. g. with a pump plate in the manner shown in Fig. 1. Thelower part of vessel 82 expands and ends in flange 83. The upper part 89of vessel 84 is cup-shaped and ends in flange 85 which is air-tightlyconnected with flange 83 by means of an interposed vacuum sealingcompound 88 and bolts 88 with nuts 81 tightened thereon. In similarmanner the lower portion of vessel 84 is expanded and ends in flangeI00, while the upper cup-shaped end ml of the next following vessel 99ends in flange I02, which is air-tightly connected with flange I00 in amanner similar to the one explained with respect to fianges 83, 85. Theadjacent and connecting portions of vessels 82, 84 and 04, 89 areobviously identical and therefore the same reference numbers are usedhenceforth for identical parts of and in them; only those within vessels82, 84 shall be described more in detail.

The lower portion of vessel 82 and the cupshaped upper portion 89 ofvessel 84 are shaped so as to confine, together with insulator 80 andits supporting ring 3|, a narrow passage 18. In particular, cup-likeportion 89 is continued to form an edge I03 of a diameter essentiallythe same or slightly larger than the innermost diameter of opening 33,i. e. the diameter of the effectfve vibrating surface. Apart from this,the shape and assembly of ring 3| with inwardly projecting rim,ring-shaped electrode 26, cylindrical piezoelectric crystal piece 24,electrode 21, spokes 22 and spring 31 in the recesses 28 and 80 ofinsulator 90, are essentially the same as described hereinbefore withreference to Figs. 1 and 2. Spring 31 and lead 92 are threaded andriveted upon pin 93 positioned within a recess of the inv sulator. Lead92 extends laterally through a narrow passage 9| in insulator 90. Lead82 continues through another insulator 94, preferably of glass orceramic material which is fitted into an opening 86 of vessel 82 andsealed therein by a suitable vacuum sealing compound 05. Lead 02 is alsosealed by such a compound into insulator 84, and. onto its outwardlyprojecting screw threaded end nuts 91, 98 are tightened, clampingbetween them terminal 50.

The top of insulator is cone-shaped and pointed, so as to permit gasmolecules to fly in the direction of arrows I04 to passage 18 and tosubstantially prevent their reflection back towards pipe I3.

Passage 18 is continued around the lower surface of ring 3| and endswith edge I08 in front of the piezo-electric vibrator 24. Hence the gasmolecules diffusing in the direction of arrows I04 are guided in thedirection of arrows I05 almost completely to the front of vibrator 24and its vibrating surface 25, impinge upon the latter and areaccelerated in the direction of arrows I00 toward insulator 90' below.Deflection of gas molecules toward and their diffusion back throughpassage I6 into space I8 back of insulator 90, is thereby prevented to alarger extent than by the structure shown in Fig. 1; passage I6 isconsiderably longer and the separation between the incoming andprojected gas molecules is improved.

The terminals SI! of the vibrator elements of both stages are assumed tobe connected with one terminal of an electrical oscillation generator,while the vessels 99 and 84 and thereby the rings III and electrodes 26in contact therewith are connected by terminal 80 to the other terminalof the generator.

In operation, and after the pre-vacuum has been established in themanner described with reference to Fig. 1, the vibrator elements 24 areactuated by switching in the oscillation generator. It is assumed inthis exemplification of the invention that the piezo-electric elementsare identical as to shape and mass and consequently ex-- citable to thesame resonance frequency which is either the fundamental or a harmonicthereof. Though the supersonic or high frequency of the vibrators isthus the same, the energy of their vibrations may be the same ordifferent, and in the latter event, e. g. the vibrating energy of thelower vibrator larger than that of the upper one. This can be obtainedby arranging in conductor I01 an adjustable resistor I08. Inversely, theupper vibrator may be more strongly excited by corresponding controlmeans. The vibrators can also be excited individually and independentlyby separate high frequency generators. The sizes or areas of theeffective vibrating surfaces 25 may be identical or different.

It will be appreciated that to the gas molecules impinging upon thevibrator surface 25 of the upper vibrator element will be imparted avelocity component directed toward the lower insulator 90, across andaway from the discharge end (gap) of passage I5 close to surface 25.Thereby the space in front of vibrating surface 25 is depleted of gasmolecules and a suction effect instantaneously produced. The gasmolecules projected from vibrating surface 25 also fly across and awayfrom the adjacent discharge end of passage I6 and are apt to produce akind of ejector effect aided by the particular shape of the dischargeend of passage I6 as shown. In any event, diffusion of gasmolecules fromspace I8 through passage I6 into space I1 results, and only a very smallfraction of the gas so diffused will revert or diffuse back throughpassage I6 into space 18.

As a result, the amount of gas molecules in space 18 and thereby thepressure therein are reduced.

The effect of vibrating surface 25' of the other. lower vibrator 24' isessentially the same as just described with reference to the uppervibrator 24, and will result in the diffusion of gas molecules projectedin the direction of arrows I05 within space 11 through passage IS in thedirection of arrows I09 into space III. The gas molecules in the latterspace are acted upon and projected by vibrating surface 25' in thedirection of arrows Hll. The gas molecules entering space III arefinally removed by the backing pump 2| connected with this space throughintake 20.

Assuming that the backing pump is capable of producing a vacuum of 0.1mm. mercury column, and assuming further that each vibrator stage of thepump can produce and maintain a ratio of pressures in the spaces infront and in 10 the back of the vibrator element or unit, equalling1000, then a pressure of 10- mm. mercury will be obtained in space l1and a pressure of 10- mm. mercury in space I8 which is a high vacuumsufficient for most applications.

In Fig, 4 a multi-stage pump is exemplified according to the invention.Similar parts used as in Fig. 3 are identified by identical referencenumbers. The uppermost or first confined space I8 is connected with amanifold H3. Bulbs (shown in dotted lines) to be evacuated are connectedwith the outlets I I4. The bulbs may be for incandescent lamps,electronic t/ubes, cathode ray tubes, etc. They are melted or sealed offafter evacuation in a well-known manner.

In this exempllfication of the invention, metal vessels 82, H5, 84 areconnected through ground with one oscillating potential of anoscillation generator, and through rings 3| and preferably ring-shapedelectrodes with each vibrator (piezoelectric element) 24, H6, 24'. Theother electrodes 21 on each of the vibrator elements are individuallyconnected through leads 92, H1, H8 with terminals 50, H9, I20, and eachterminal is individually connected through conductors I2I, I22, I23 withequal or different potentials of the oscillation generator. Thesedifferent potentials may be derived either from a single oscillatorycircuit by tapping therefrom different voltages, or from differentcircuits which may also be tuned to different frequencies. Thereby thevibrator elements can be excited with different energies and/or todifferent supersonic frequencies. When different frequencies are appliedto the vibrator elements, their thicknesses must be different in orderto respond in resonance to those exciting frequencies; if thethicknesses are identical, higher harmonics can be used for excitation.

It will be appreciated that in the lowest or last confined space I 24the highest of the low pressures is produced and maintained by means ofan auxiliary or backing pump. The low pressures in the spaces I25, I26and I8 will decrease in the order named so as to produce the lowestpressure or the highest vacuum in space I8 communicating with theinterior of manifold H3 and the containers (bulbs) communicatingtherewith.

It is to be understood that by increasing the number of the vibratorpump stages, the ultimate vacuum attained in space I8 can be increasedand, e. g. with three such stages, vacua of 10- mm. mercury column, orless, attained within a short period of time.

It should be understood that the invention is not Iimited in any way tothe exemplifications shown or any theory propounded herein, but is to bederived in its broadest aspects from the appended claims. Variouschanges can be made within that scope. Thus, instead of piezo-electricelements exemplified herein in their most simple form, piezo-electricvibrator units can be used comprised of one or more properly cut Piecesof piezo-electric material (quartz) and cemented upon or between platesof metal (particularly steel) one of which forms the exposed surface(25). Reference is made in this respect to the description andillustrations in my copending application Ser, No. 500,242. Instead ofthe use of illustrated in my said copending application with 1. In amethod of rarefying gas in a first '06.-

fined space co :nmunicating with a second confined space, the steps ofproducing and maintaining in the gas in said second space a moderatelyreduced pressure, producing energy vibrations at supersonic highfrequency, and applying the vibrational energy in a mean direction awayfrom said first space to gas molecules in said second space to impart tosaid gas -.molecules velocity components in said direction away fromsaid first space and cause diffusion of gas molecules from said firstinto said second space resulting in rareiaction of the gas'in said firstspace.

2. In a method of rarefying gas in a first confined space communicatingthrough a narrow passage with a second confined space, the steps ofproducing and maintaining in the gas in said second space a moderatelyreduced pressure of a value at which the mean free path of the gasmolecules exceeds the dimensions of said passage, producing energyvibrations at supersonic high frequency, and applying the vibrationalenergy in a mean direction away from said first space to gas moleculesin said second space to impart velocity components to said gas moleculesessentially in said direction and promote diffusion of gas moleculesthrough said passag from said first into said second space resulting inrareexciting said vibrator and thereby its exposed surface element tovibrations of supersonic frequency in a direction essentially away fromsaid discharge and and perpendicular to said surface element.

4. In a method of reducing the pressure in the gas contained in aseries-arrangement of at least three confined spaces including a firstand a last space and communicating through narrow passages arrangedbetween each adjacent pair of them, in the first of which the lowestpressure is to be produced, the steps of producing and maintaining inthe gas in the last of said spaces a pressure at a level at which themean free path of the gas molecules exceeds the dimensions of saidpassages, producing energy vibrations at supersonic high frequency insaid second to last spaces and in a direction away from an adjacentpassage of lower order number, and applying the vibrational energy togas molecules in each of said second to last spaces and close to thedischarge end of a passage to impart velocity components to gasmolecules in each of said second to last spaces in said direction andpromote diffusion of gas molecules through each of said passages from aconnected space of lower order number into that of next higher ordernumber, resulting in reduction of pressure in the gas in each space from12 which it diffuses and lowest pressure in the gas in the first space.

5. In a method of rarefying gas in a first confined space communicatingthrough a narrow passage with a second confined space, the steps ofprerarefying the gas in said second space to a degree at which the meanfree path of the gas molecules exceeds the dimensions of said passage,producing energy vibrations at supersonic high frequency close to thedischarge end of said passage and in a direction away from saiddischarge end, and applying the vibrational energy to gas molecules insaid second space to impart velocity components in said direction tosaid gas molecules in said'second space and locally deplete of gasmolecules a portion of said second space where said vibrations areproduced close to said discharge end, resulting in diffusion of gasmolecules through said passage from said first into said second spacetoward its depleted portion and increased rarefaction of the gas in saidfirst space.

6. In a method of producing a difference of high vacuum pressure in gasconfined in a first and a second space which communicate through anarrow passage, the steps of prerarefying the gas in said communicatingspaces to a degree at which the mean free path of the gas moleculesexceeds the dimensions of said passage, producing energy vibrations atsupersonic high frequency and in a direction away from said passage andfirst space, and applying the vibrational energy to gas molecules insaid second spac to impart velocity components to said acted upon gasmolecules in said direction away from said passage resulting inpromotion of diffusion of gas molecules through said passage from saidfirst into said second space and increased rarefaction of the gas insaid first space.

7. In apparatus for producing a high vacuum in a container by means of amolecular high vacuum pump and an auxiliary vacuum pump, a high vacuumpump essentially comprising a first confined space communicating througha narrow passage with a second confined space and said auxiliary pump,the dimensions of said passage smaller than the mean free path of thegas molecules at the reduced pressure to be produced by said auxiliarypump, a plezo-electric vibrator unit arranged in said second space closeto the discharge end of said passage, said unit provided with a surfaceelement exposed towards said second space and capable of vibratingessentially in a direction perpendicular to its exposed surface and awayfrom said passage and first space, and electrical means for applyingoscillatory electric energy of selected supersonic frequency to saidvibrator unit for exciting it and thereby its surface element tomechanical vibrations of said frequency or a harmonic thereof andessentially in said direction.

8. An apparatus for producing a high vacuum in a container, essentiallycomprising a vessel the interior of which is subdivided in a first andsecond space communicating through a nar- 'i'ow gap, means forconnecting said first space of the vessel with a, container to beevacuated,

means for connecting said second space of th vessel with a pre-vacuumpump, a mechanical vibrator capable of being electrically excited tovibrations of selected supersonic frequency mounted within said vesseland provided with an exposed surface element arranged close to said gapand facing said second space, said surface element capable of vibratingin a direction essentially perpendicular toit, and electrically con--ductive means for connecting said vibrator with a source of oscillatoryelectrical energy of said selected supersonic frequency. 9. An apparatusfor producing a high vacuum in a gas within confined space, including avessel the interior of which is subdivided in a first and second spacecommunicating through a narrow gap, means for connecting said firstspace with the confined space to be evacuated, means for connecting saidsecond space of the vessel with a pre-vacuum pump, the dimensions ofsaid gap being smaller than the mean free path of the molecules of saidgas at pre-vacuum pressure to be produced by said pump, a piezo-electricvibrator element capable of being excited to mechanical vibrations ofselected high frequency within said vessel, means as exemplified by anelectrical insulator supporting and covering said vibrator element butleaving exposed a surface element of it, said surface element close tosaid gap and facing said second space, said vibrator element capable ofvibrating in a, direction essentially perpendicular to said surface, andelectricallly conductive means for connecting said vibrator element witha source of electrical oscillatory energy of said selected highfrequency. 10. An apparatus for producing a high vacuum in a gas inwithin confined space, including an elongated vessel, at least onepiezo-electric vibrator element capable of being excited to mechanicalvibrations of selected supersonic frequency, means as exemplified by anelectrical insulator for supporting within said vessel and covering saidvibrator element but leaving exposed a surface element of it, saidvibrator element and supporting means arranged within said vessel so asto leave a narrow gap between them and said vessel, said surface elementcapable of vibrations in a direction essentially perpendicular to it,

electrically conductive means for connecting said.

vibrator element with a source of electric oscillatory energy of saidselected supersonic frequency, means in the back of said supportingmeans for connecting in open communication said vessel with a containerto be evacuated, and means in front of said vibrator element and itsexposed surface element for connecting in open communication said vesselwith another pump space.

11. For use with a container of gas to be rarefied and a pre-v'acuumpump, an elongated vessel open at opposite ends, the first of said Iends to be connected with the container and the second of said ends tobe connected with the pre-vacuum pump, said vessel comprising at leasttwo spaces communicating through a narrow passage, the first of saidspaces communicating with said first end and the second of said spacescommunicating with said second end, a mechanical vibrator capable ofbeing electrically excited to vibrations of supersonic high frequencymounted within said vessel between said spaces and surrounded by saidpassage, said vibrator having a surface element arranged close to saidpassage and-facing and exposed to said second space, said surfaceelement capable of vibrating in a direction essentially perpendicular toit, and electrically conductive means for connecting said vibrator witha source of oscillatory electrical energy for exciting said vibrator.

12. The combination including a container for gas to be rarefied, apre-vacuum pump, and a vessel, said vessel at a first placecommunicating with said container and at another second placecommunicating with said vacuum pump, said vessel comprising at least twospaces communicating through a narrow passage, the first of said spacescommunicating with said first place and the sec-- ond of said spacescommunicating with said second place, a mechanical vibrator capable ofbeing electrically excited to vibrations of supersonic high frequencymounted within said vessel and provided with an exposed surface elementarranged close to said passage and facing said second space, saidsurface element capable of vibrating in a directionessentiallyperpendicular to it and away from said passage and first space, andelectrically conductive means for connecting said vibrator with a sourceof oscillatory electrical energy for exciting said vibr tions.

13. The combination including a container for as to be rarefied, apre-vacuum pump, a source of oscillatory electrical energy, and avessel, said vessel at a first place communicating with said containerand at another, second place communicating with said pre-vacuum pump,said vessel comprising at least two spaces communicating through anarrow passage, the first of said spaces communicating with said firstplace and the second of said spaces communicating with said secondplace, a mechanical vibrator capabl of being electrically excited tovibrations of supersonic high frequency mounted within said vessel andprovided with an exposed surface element arranged close to said passageand facing said second space, said surface element capable of vibratingin a direction essentially perpendicular to it and away from saidpassage and first space, and electrically conductive means forconnecting said vibrator with said source of oscillatory electricalenergy, said ocillatory energy adapted to excite said vibrations.

14. In a method of rarefying gas in a first confined space communicatingWith a, second confined space, the steps of producing and maintaining inthe gas in the second space a maximum pressure of about 10- millimetersmercury column, producing energy vibrations at a frequency of about100,000 to 10,000,000 cycles per second in a direction away from saidfirst space, and applying the vibrational energy to gas molecules insaid second space to impart velocity components to said molecules insaid direction and thereby cause difiusion of gas molecules from saidfirst into said second space, whereby the gas in said first space may berarefied and its pressure reduced to below about 10" millimeters mercurycolumn.

ADOLPH H. ROSENTHAL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

